Positive photoresist having improved processing properties

ABSTRACT

Polymers having a molecular weight (weight average) M w  from 10 3  to 10 6 , comprising recurring structural units of the formulae (I), (IIa) and (IIb) ##STR1## in which R 1  is hydrogen or methyl, Y is a direct bond or a divalent radical of the formula (III) ##STR2## in which Z is a C 1  -C 6  alkylene group bound to the phenyl nucleus, 
     OR 2  is an acid-cleavable radical, 
     in which R 2  is C 4  -C 10  tert-alkyl, allyl, cyclohex-2-enyl, C 6  -C 14  aryl or C 7  -C 16  aralkyl which are unsubstituted or mono- or poly-substituted by C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, trialkylsilyl or a group of the formulae (IV)-(VII) ##STR3## in which R 8  is C 1  -C 6  alkyl, or C 6  -C 14  aryl or C 7  -C 16  aralkyl which are unsubstituted or mono- or poly-substituted by C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, 
     R 3  and R 4  independently of one another are hydrogen, C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, 
     R 5  and R 6  independently of one another are hydrogen or methyl, 
     X is C 1  -C 6  alkylene and R 7  is C 1  -C 6  alkyl, or C 6  -C 14  aryl or C 7  -C 16  aralkyl which are unsubstituted or mono- or poly-substituted by C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms, or is --CO--R 8  in which R 8  is as defined in formula (IV), are suitable for use in DUV positive photoresists which show greatly reduced delay time effects and are distinguished by a high thermal stability and high resolution capacity.

The present invention relates to polymers based on derivatives of styrene and maleimide, to radiation-sensitive compositions containing these polymers, to the use of such compositions as positive photoresist and to the protective layers and relief structures produced from these compositions.

Lithography in the deep UV region (DUV, wavelengths of about 200-300 nm) is particularly suitable for producting relief structures in the submicron range.

EP-A 410 794, negative DUV photoresists are described which comprise specific acid-hardenable copolymers and terpolymers based on styrene and hydroxymaleimides. These negative resists can be developed under aqueous-alkaline conditions.

In general, however, positive photoresists are more suitable for producing images of certain geometrical structures, for example isolated lines, equidistant lines or interspacious or contact holes, and they are usually preferred for such applications over comparable negative resists.

Positive photoresist compositions based on poly[p-tert-butoxycarbonyloxystyrene] and onium salts, suitable for lithography in the UV region, are known, for example, from U.S. Pat. No. 4,491,628.

Similar resist formulations comprising poly[p-2-tetrahydropyranyloxy]styrene are described in EP-A 342 498.

However, these chemically intensified positive photoresists show, as a function of the so-called delay time, structural changes which manifest themselves in more or less pronounced T-shaped profiles (T-topping) of the developed structures. Delay time signifies the time difference between exposure and the subsequent post-exposure bake which is as a rule necessary in order to ensure complete reaction of the acid-sensitive groups with the acid generated by the exposure.

Traces of organic bases in the surrounding atmosphere are probably responsible for these delay time effects. In "Deep-UV Resists with improved delay capacities", SPIE Volume 1672 (Adv. Resist Technol. Process.), 46-55 (1992), D. J. H. Funhoff, H. Binder and R. Schwalm discuss various measures for suppressing this undesired effect, for example the application of an additional protective coating, an expensive filtration of the air, or the use of special developers for removing the T-tops, and finally recommend the use of specific additives. The stability, achieved in this way, towards delay time effects involves, however, a certain loss of sensitivity.

It has now been found that, when specific polymers based on derivatives of styrene and maleimide are used as photoresist materials, the delay time effects described above are largely suppressed without addition of additives or the insertion of additional process steps.

The present invention relates to polymers having a molecular weight (weight average) M_(w) from 10³ to 10⁶, comprising recurring structural units of the formulae (I), (IIa) and (IIb) ##STR4## in which R₁ is hydrogen or methyl, Y is a direct bond or a divalent radical of the formula (III) in which Z is a C₁ -C₆ alkylene group bound to the phenyl nucleus,

OR₂ is an acid-cleavable radical,

in which R₂ iS C₄ -C₁₀ tert-alkyl, allyl, cyclohex-2-enyl, C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, trialkylsilyl or a group of the formulae (IV)-(VII) ##STR5## in which R₈ is C₁ -C₆ alkyl, or C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are substituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms,

R₃ and R₄ independently of one another are hydrogen, C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms,

R₅ and R₆ independently of one another are hydrogen or methyl,

X is C₁ -C₆ alkylene and R₇ is C₁ -C₆ alkyl, or C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, or is --CO--R₈ in which R₈ is as defined in formula (IV).

R₁ is preferably hydrogen.

Y is preferably a direct bond.

Alkyl or alkoxy groups R₂, R₃, R₄, R₇ or R₈, or alkyl or alkoxy groups as substituents of allyl, cyelohex-2-enyl, aryl or aralkyl groups can be straight-chain or branched. Examples are: methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, neopentoxy and n-hexoxy.

Halogen atoms as radicals R₃ or R₄, or as substituents of allyl, cyclohex-2-enyl, aryl or aralkyl groups, are preferably bromine or chlorine atoms.

Unsubstituted or substituted aryl or aralkyl groups R₂, R₇ or R₈ are, for example, phenyl, tolyl, xylyl, mesityl, isityl, naphthyl, anthryl, phenanthryl, fluorenyl, biphenyl, benzyl, 2-phenylethyl, 2-phenylprop-2-yl or tolylmethyl.

Unsubstituted or substituted allyl groups R₂ are preferably allyl, methallyl or especially 3-methylbut-2-enyl. C₁ -C₆ Alkylene groups Y or X can likewise be straight-chain or branched. Examples are methylene, ethylene, propylene, 2,2-propanediyl, trimethylene, tetramethylene and hexamethylene.

Preferred polymers according to the invention comprise recurring structural units of the formula (I) in which R₁, R₃ and R₄ are hydrogen, Y is a direct bond and R₂ is C₄ -C₁₀ tert-alkyl, trimethylsilyl, allyl which is unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, cyclohex-2-enyl or a group of the formulae (IV)-(VII) in which R₈ is C₁ -C₄ alkyl or phenyl.

Particularly preferred are polymers comprising recurring structural units of the formula (I) in which R₁, R₃ and R₄ are hydrogen, Y is a direct bond and R₂ is tert-butyl, tert-butoxycarbonyl, 3-methylbut-2-enyl or a group of the formula (V).

In the structural units of the formula (IIa), R₅ and R₆ are preferably hydrogen and X is preferably methylene.

Also preferred are polymers comprising recurring structural units of the formula (IIb) in which R₅ and R₆ are hydrogen, R₇ is C₁ -C₄ alkyl, phenyl or --CO--R₈, in which R₈ is C₁ -C₄ alkyl or phenyl, and X is methylene, ethylene, trimethylene or tetramethylene.

Particularly preferred are polymers comprising recurring structural units of the formula (IIb) in which R₅ and R₆ are hydrogen, R₇ is methyl or acetyl and X is methylene or ethylene.

The polymers according to the invention preferably comprise 10-75 mol %, in particular 20-50 mol %, of structural units of the formula (IIa) and 25-90 mol %, in particular 50-80 mol %, of structural units of the formula (IIa), relative to 100 mol % structural units of the formula (I).

The molecular weight (weight average) of these polymers is preferably 5000-500 000, in particular 20 000-250 000.

The polymers according to the invention can be prepared in a known manner by free-radical polymerization of compounds of the formulae (IX), (Xa) and (Xb) ##STR6## in which R₁ to R₈, Y and X are as defined above.

The free-radical copolymerization can be carried out with application of various techniques. These have been described, for example, by S. Sandler and W. Karo in "Polymer Synthesis", Volume 1, pages 3-17, 1968, Academic Press, New York. Examples of usual polymerization processes are the polymerization in bulk or in solvents, and also emulsion polymerization, suspension polymerization or precipitation polymerization. If desired, the molecular weight can be adjusted by the addition of small quantities of a regulator (for example dodecylmercaptan).

The starting products of the formulae (IX), (Xa) and (Xb) are known or can be prepared by known methods.

The compounds of the formula (IX), in which Y is a direct bond and R₂ is C₁ -C₆ alkyl, C₁ -C₆ alkoxy, C₆ -C₁₄ aryl, C₇ -C₁₅ aralkyl, trimethylsilyl or C₂ -C₈ alkenyl, can be obtained, for example, by condensation of unsubstituted or substituted p-hydroxystyrene or α-methyl-p-hydroxystyrene with the corresponding alkyl, alkoxy, aryl, aralkyl, trimethylsilyl or alkenyl halites or tosylates in the presence of bases.

Analogously, compounds of the formula (IX), in which Y is a direct bond and R₂ is a group of the formula (IV), are accessible from unsubstituted or substituted p-hydroxystyrene or α-methyl-p-hydroxystyrene and the corresponding chlorocarbonates.

The compounds of the formula (IX), in which Y is a direct bond and R₂ is a group of the formulae (V)-(VII), can be synthesized, for example, from unsubstituted or substituted p-hydroxystyrene or α-methyl-p-hydroxystyrene by reaction with 2,3-dihydropyran, 5-alkoxy-, 5-aryloxy- or 5-aralkoxy-2,3-dihydropyran or 2,3-dihydrofuran in acid solution.

The compounds of the formula (IX), in which Y is a divalent radical of the formula (III), can be prepared analogously from the corresponding acrylates or methacrylates.

Examples of suitable compounds of the formula (IX) are 4-methoxystyrene, α-methyl-4-methoxystyrene, 4-ethoxystyrene, 4-tert-butoxystyrene, 4-phenoxystyrene, 4-benzyloxystyrene, 4-trimethylsilyloxystyrene, 4-allyloxystyrene, 4-methallyloxystyrene, 4-(tert-butylcarbonyloxy)styrene, 4-(2-tetrahydropyranyloxy)styrene, 4-(2-tetrahydrofuranyloxy)styrene, 4-(3-methylbut-2-enyloxy)styrene, 4-(2-tetrahydropyranyloxy)benzyl methacrylate and 4-(2-tetrahydropyranyloxy)benzyl acrylate.

The compounds of the formulae (Xa) and (Xb) are likewise known or can be prepared by known processes from maleimide or methyl- or dimethyl-maleimide, for example by reacting maleimide in the presence of bases with a halide or a tosylate of the formula LG--X--OH or LG--X--OR₇, in which X and R₇ are as defined above and LG is halogen or CH₃ --C₆ H₄ --SO₃.

The synthesis of N-hydroxymethylmaleimide from maleimide and formaldehyde in the presence of NaOH is described, for example, in EP-A 410 794.

Examples of suitable compounds of the formulae (Xa) and (Xb) axe N-hydroxymethylmaleimide, N-2-hydroxyethylmaleimide, N-3-hydroxypropylmaleimide, N-4-hydroxybutylmaleimide, N-(2-hydroxyprop-2-yl)maleimide, N-methoxymethylmaleimide, N-phenoxymethylmaleimide, N-benzyloxymethylmaleimide, N-2-methoxyethylmaleimide, N-3-methoxypropylmaleimide, N-4-methoxybutylmaleimide, N-acetoxymethylmaleimide and N-(2-acetoxyethyl)maleimide.

The polymerization is in general initiated by a conventional free radical starter. These include thermal initiators such as azo compounds, for example α,α'-azoisobutyronitrile (AIBN), or peroxides, for example benzoyl peroxide, or redox initiator systems such as a mixture of iron(III) acetylacetonate, benzoin and benzoyl peroxide, or photochemical free-radical formers such as benzoin or benzil dimethylketal.

The polymerization is preferably carried out in solution. The reaction temperature is in general in the range from 10° to 200° C., preferably between 40° and 150° C., particularly preferably between 40° and 100° C.

Solvents which may be present must be inert under the reaction conditions. Possible solvents are, inter alia, aromatic hydrocarbons, chlorinated hydrocarbons, ketones and ethers. Examples are: benzene, toluene, xylenes, ethylbenzene, isopropylbenzene, ethylene chloride, propylene chloride, methylene chloride, chloroform, methyl ethyl ketones, acetone, cyclohexanone, diethyl ether or tetrahydrofuran.

As mentioned at the outset, the polymers according to the invention are very suitable as base resins for DUV positive photoresists, which show greatly reduced delay time effects and have a high resolution capacity and high thermal stability.

The invention thus also relates to radiation-sensitive compositions comprising

a) at least one polymer according to the invention as defined above and

b) at least one compound which forms an acid under the action of actinic radiation.

Preferably, the compositions according to the invention comprise as further component c) a solvent or a solvent mixture.

Moreover, the compositions according to the invention can comprise solution inhibitors, which reduce the solubility of the composition in conventional alkaline developers, but which are cleaved under the action of acid in such a way that the remaining reaction products are soluble in the developer. Such solution inhibitors are known to those skilled in the art and are described, for example, in EP-A 329 610 and EP-A 475 903.

The compounds b), which form an acid under the action of actinic radiation, can especially be onium salts, such as diazonium salts, sulfonium salts, sulfoxonium salts and iodonium salts, and also disulfones. Preferred are sulfonium salts of the formula VIII

    (Ar.sub.1).sub.q (Z.sub.1).sub.r (Z.sub.2).sub.s S.sup.⊕ X.sup.63(VIII),

in which

Ar₁ is phenyl, naphthyl or phenyl--COCH₂ --, which are unsubstituted or substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, --OH and/or nitro,

Z₁ is C₁ -C₆ alkyl or C₃ -C₇ cycloalkyl and

Z₂ is tetrahydrothienyl, tetrahydrofuryl or hexahydropyryl,

q is0, 1, 2 or3,

r is 0, 1 or 2 and

s is 0 or 1, the sum q+r+s being 3, and

X₁.sup.⊖ is a chloride, bromide or iodide anion, BF₄.sup.⊖, PF₆.sup.⊖, AsF₆.sup.⊖, SbF₆.sup.⊖, FSO.sup.⊖ or the anion of an organic sulfonic acid or carboxylic acid.

Phenyl, naphthyl and phenacyl groups Ar₁ are preferably monosubstituted, in particular by Cl, Br, methyl, methoxy, --OH or nitro. Particularly preferably, these radicals are unsubstituted. Z₁ is preferably C₁ -C₄ alkyl, especially methyl or ethyl. Preferably, q is 2 or 3, r is 1 or zero and s is zero, and especially q is 3, and r and s are zero. Very particularly preferably, Ar₁ is unsubstituted phenyl and q is 3.

The anion X₁.sup.⊖ of an organic sulfonic acid or carboxylic acid can be the anion or aliphatic, cycloaliphatic, carbocyclic-aromatic, heterocyclic-aromatic or araliphatic sulfonic or carboxylic acids. These anions can be substituted or unsubstituted. Sulfonic and carboxylic acids of low nucleophily are preferred, for example partially fluorinated or perfluorinated derivatives or derivatives which are substituted in the position vicinal to the particular acid group. Examples of substituents are halogen such as chlorine or especially fluorine, alkyl such as methyl, ethyl or n-propyl, or alkoxy such as methoxy, ethoxy or n-propoxy.

Examples of aliphatic sulfonic acids are methane-, ethane-, n-propane-, n-butane- and n-hexane-sulfonic acid or the corresponding partially fluorinated or perfluorinated derivatives.

Examples of aliphatic carboxylic acids are formic acid, acetic acid, propionic acid, butyric acid, pivalic acid, caproic acid, 2-ethylhexylcarboxylic acid and fatty acids such as lauric acid, myristic acid or stearic acid, and also the partially fluorinated or perfluorinated derivatives of these acids.

Examples of cycloaliphatic sulfonic or carboxylic acids are cyclohexanesulfonic acid, cyclohexanecarboxylic acid, camphor-10-sulfonic acid or partially fluorinated or perfluorinated derivatives thereof.

Examples of carbocyclic-aromatic sulfonic acids are benzenesulfonic acid, toluenesulfonic acid, ethylbenzenesulfonic acid, isopropylbenzenesulfonic acid, dodecylbenzenesulfonic acid or dimethylbenzenesulfonic acid, 2,4,6-triisopropylbenzenesulfonic acid, 2,4,6-trimethylbenzenesulfonic acid, naphthalene-mono-, -di- or -tri-sulfonic acids and the corresponding alkylated or partially fluorinated or perfluorinated derivatives of these sulfonic acids.

Examples of heterocyclic-aromatic sulfonic acids axe pyridine-, thiophene- or pyrrole-sulfonic acids and the corresponding partially fluorinated or perfluorinated derivatives of these acids.

Examples of araliphatic sulfonic acids are benzylsulfonic acid, α-methylbenzylsulfonic acid and the corresponding partially fluorinated or perfluorinated derivatives of these compounds.

Examples of carbocyclic aromatic carboxylic acids are benzoic acid, toluenecarboxylic acid, ethylbenzenecarboxylic acid, isopropylbenzenecarboxylic acid or dimethylbenzenecarboxylic acid, naphthalenecarboxylic acid or anthracenecarboxylic acid and the corresponding partially fluorinated or perfluorinated derivatives of these compounds.

Examples of heterocyclic-aromatic carboxylic acids are pyridine-, thiophene- or pyrrolecarboxylic acid and the corresponding partially fluorinated or perfluorinated derivatives of these compounds.

Examples of araliphatic carboxylic acids are benzylcarboxylic acid, α-methylbenzylcarboxylic acid and cinnamic acid as well as the corresponding partially fluorinated or perfluorinated derivatives of these compounds.

Preferably, X₁.sup.⊖ is the monovalent anion of an organic sulfonic acid, in particular of a partially fluorinated or perfluorosulfonic acid. These anions are distinguished by a particularly low nucleophily.

Specific examples of suitable sulfonium salts of the formula VIII are triphenylsulfonium bromide, triphenylsulfonium chloride, triphenylsulfonium iodide, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluoroarsenate, triphenylsulfonium trifluoromethanesulfonate, diphenylethylsulfonium chloride, phenacyldimethylsulfonium chloride, phenacyltetrahydrothiophenium chloride, 4-nitrophenacyltetrahydrothiophenium chloride and 4-hydroxy-2-methylphenylhexahydrothiopyrylium chloride. Triphenylsulfonium trifluoromethanesulfonate is particularly preferred.

The compounds b) used can also be iodonium salts of the formula (XI)

    [Ar.sub.2 --I.sup.⊖ --Ar.sub.3 ]X.sub.2 .sup.⊕ (XI)

in which

Ar₂ and Ar₃ independently of one another are phenyl or naphthyl which are unsubstituted or substituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy, halogen and/or nitro, or Ar₂ and Ar₃ together are a group of the formula (XII) ##STR7## in which Z₃ is C₁ -C₄ alkyl, C₁ -C₄ alkoxy, halogen or nitro and

Q is a direct bond, --O--, --CH₂ -- or --CO-- and

X₂.sup.⊖ is as defined for X₁.sup.⊖ in the formula (VIII). [Iodonium salts of the formula (XI) are described, for example, in GB-A 1 539 192.

Suitable compounds b) are also substances of the formulae (XIII) to (XXII), which generate sulfonic acid under the action of actinic radiation, ##STR8## in which t is 1 or 2, preferably 1,

Z₄ is phenyl or napthyl which are mono- to tri-substituted --Cl, --Br, --CN, --NO₂, C₁ -c₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄ alkylthio, phenoxy, phenylthio, C₁ -C₄ alkylamino, C₂ -C₄ dialkylamino or benzoyl, in particular phenyl which is unsubstituted or monosubstituted by --Cl, methyl or methoxy,

Z₅ is hydrogen or C₁ -C₄ alkyl and

Z₆ is hydrogen, C₁ -C₄ alkyl or phenyl or

Z₅ and Z₆ form, together with the linking C atom, a cyclopentane ring or cyclohexane ring,

Z₇, with t=1, is C₁ -C₁₈ alkyl, phenyl or naphthyl, which are unsubstituted or substituted by C₁ -C₄ alkyl, cyclopentyl, cyclohexyl or camphoryl and with t=2 is C₂ -C₈ alkylene or phenylene,

Z₈ is phenyl or naphthyl which are unsubstituted or mono- to tri-substituted by --Cl, --Br, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄ alkylthio, phenyl, phenoxy, phenylthio, C₁ -C₄ alkyl-CONH--, benzoylamino or dimethylamino, in particular phenyl which is unsubstituted or monosubstituted by --Cl, C₁ -C₄ alkoxy, methylthio or phenyl,

Z₉ is --OH or C₁ -C₄ alkyl,

Z₁₀ is C₁ -C₄ phenyl,

Z₁₁ is hydrogen, C₁ -C₄ alkyl, furyl or --CCl₃ or

Z₁₀ and Z₁₁, together with the linking C atom, form a cyclopentane ring or cyclohexane ring,

Z₁₂ and Z₁₃ independently of one another are phenyl which is unsubstituted or substituted by halogen, C₁ -C₄ alkyl or C₁ -C₄ alkoxy,

Z₁₄ is hydrogen or C₁ -C₄ alkyl,

Z₁₅, with t=1, is C₁ C₆ alkyl, phenyl, naphthyl or benzyl and, with t=2, is C₁ -C₆ alkylene, phenylene or xylylene,

Z₁₆ is phenylene or naphthalene, which are unsubstituted or substituted by halogen, nitro, C₁ -C₄ alkyl, C₁ -C₄ alkoxy or C₁ -C₄ alkylthio or --CH═CH--, Z₁₇, with t=1, is C₁ -C₁₂ alkyl, which is unsubstituted or substituted by halogen, nitro, C₁ -C₄ alkyl or C₁ -C₄ alkoxy or phenyl which is unsubstituted or substituted by halogen, nitro, C₁ -C₄ alkyl or C₁ -C₄ alkoxy, and, with t=2, is C₂ -C₈ alkylene or phenylene,

Z₁₈ is phenyl or napthyl which are unsubstituted or substituted by halogen, nitro, --CN, C₁ -C₄ alkyl, methoxy, ethoxy, dimethylamino or benzoyl, and the Z₁₉ independently of one another are C₁ -C₄ alkyl,

R₉ is C₁ -C₁₂ alkyl which is unsubstituted or substituted by halogen, nitro, C₁ -C₄ alkyl or C₁ -C₄ alkoxy, or phenyl which is unsubstituted or substituted by halogen, nitro, C₁ -C₄ alkyl or C₁ -C₄ alkoxy,

R₁₀ is C₁ -C₄ alkyl, C₁ -C₄ alkoxy or phenyl.

R₁₁ and R₁₂ independently of one another are C₁ -C₄ alkyl, C₁ -C₄ alkoxy or phenyl or together are radical of the formulae (XXIII), (XXIV) or (XXV) ##STR9## and R₁₃ is C₁ -C₄ alkyl, C₁ -C₄ alkoxy, phenyl, benzoyl. Alkyl, alkoxy, alkylthio, alkylamino, dialkylamino, alkylcarbamoyl and alkylene groups according to the definition can be straight-chain or branched, but are preferably straight-chain. Halogen is in particular --Cl or --Br.

Compounds of the formulae (XIII) to (XXII) are described, for example, in EP-A 0 166 682 and 0 085 024 and in the literature cited therein. Particularly preferred compounds of the formulae (XIII) to (XXII) are phenacyl p-methylbenzenesulfonate, benzoin p-toluenesulfonate, α-(p-toluenesulfonyloxy)methylbenzoin-3-(p-toluenesulfonyloxy)-2-hydroxy-2-phenyl-1-phenylpropylether, N-(p-dodecylbenzenesulfonyloxy)-1,8-naphthalimide and N-(phenylsulfonyloxy)-1,8-naphthalimide.

Further suitable compounds b) are o-nitrobenzaldehydes which rearrange under actinic radiation into o-nitrosobenzoic acids, such as 1-nitrobenzaldehyde and 2,6-dinitrobenzaldehyde; α-halogenoacylphenones such as α, α, α-trichloroacetophenone and p-tert-butyl-α, α, α-trichloroacetophenone, and also sulfonic acid esters of o-hydroxyacylphenones such as 2-hydroxybenzophenone methanesulfonate and 2,4-hydroxybenzophenone bis(methanesulfonate).

Finally, suitable compounds b) are also those which comprise aromatically bound chlorine or bromine, such as are described, for example, in EP-A0 3 18 649, for example compounds of the formula (XXVI) ##STR10## with at least one aromatically bound chlorine or bromine atom, in which, for example, p is 0 or 1.

Z₂₀ is --COOH, --OZ₂₃ or --SZ₂₃,

Z₂₁ and Z₂₂ independently of one another are hydrogen, --Cl, --Br, alkyl which is unsubstituted or substituted by aryl, alkoxy, aryloxy, --OH or --F, or aryl which is unsubstituted or substituted by alkoxy, aryloxy, --OH or halogen,

Z₂₃ is hydrogen, alkyl or aryl which are unsubstituted or substituted analogously to Z₂₁, or acryl,

A, with p=0, is hydrogen, --Cl, --Br or alkyl which is unsubstituted or substituted analogously to Z₂₁, and, with p=1, is --SO₂ --, propylene or perfluoroalkylene and B is a group ##STR11## alkylcarbonyl, alkoxycarbonyl or substituted sulfonylimidocarbonyl.

Examples of such compounds are hexafluorotetrabromobisphenol A, 1,1,1-tris-(3,5-dibromo-4-hydroxyphenyl)ethane and N(2,4,6-tribromophenyl)-N'-(p-toluenesulfonyl)urea.

Compounds b) which are used with particular preference are those of the formula (VIII), in which Ar₁ is phenyl, q is the number 3, r and s are zero, and X₁.sup.⊖ is SbF₆.sup.⊖, AsF₆.sup.⊖, PF₆.sup.⊖, CF₃ SO₃.sup.⊖, C₂ F₅ SO₃.sup.⊖, n-C₃ F₇ SO₃.sup.⊖, n-C₄ F₉ SO₃.sup.⊖, n-C₆ F₁₃ SO₃.sup.⊖, n-C₈ F₁₇ SO₃.sup.⊖ or C₆ F₅ SO₃.sup.⊖.

Very particularly preferably, the component b) used is triphenylsulfonium trifluoromethanesulfonate.

The compounds b) are advantageously employed in a quantity of 0. 1-20% by weight, preferably 1-10% by weight and especially 1-6% by weight, relative to the weight of component a).

The compositions according to the invention can comprise further conventional additives, for example binders, stabilizers, pigments, dyes, fillers, adhesion promoters, flow agents, wetting agents and plasticizers. Preferably, the compositions are dissolved in suitable solvents [component c)] for application.

The binder is selected according to the field of application and the properties demanded for this purpose. Examples of suitable binders are novolaks which are derived from an aldehyde, preferably formaldehyde, acetaldehyde or furfuraldehyde, but in particular from formaldehyde, and a phenol. The phenolic component of these binders is preferably phenol itself, or also halogenated phenol, for example substituted by one to two chlorine atoms, preferably p-chlorophenol, or it is a phenol substituted by one to two C₁ -C₉ alkyl groups, for example o-, m- or p-cresol, a xylenol, p-tert-butylphenol or p-nonylphenol. However, the phenol component of the preferred novolaks can also be p-phenylphenol, resorcinol, bis(4-hydroxyphenyl)methane or 2,2-bis(4-hydroxyphenyl)propane.

Examples of further suitable binders are copolymers of maleic anhydride with styrene, vinyl ethers or 1-alkenes. Homopolymeric or copolymeric acrylates and methacrylates, for example copolymers of methyl methacrylate/ethyl acrylate/methacrylic acid, poly(alkyl methacrylates) or poly(alkyl acrylates) having, for example, 1-20 carbon atoms in the alkyl radical, can also be used as binders.

Preferably, the binder used is an alkali-soluble substance, for example a novolak (if appropriate, modified as described above), poly(4-hydroxystyrene) or poly(4-hydroxy-3,5-dimethylstyrene), copolymers of maleic anhydride with styrene, vinyl ethers or 1-alkenes, and also copolymers of acrylate or methacrylate esters with ethylenically unsaturated acids, for example methacrylic acid or acrylic acid.

The radiation-sensitive compositions according to the invention, dissolved in a solvent or solvent mixture, are outstandingly suitable as coating agents for substrates of any type, for example wood, textiles, paper, ceramics, glass, plastics such as polyester, polyethylene terephthalate, polyolefins or cellulose acetate, in particular in the form of films, and also metals such as Al, Cu, Ni, Fe, Zn, Mg or Co, and GaAs, Si or SiO₂ to which an image is to be applied by imagewise expose.

The selection of the solvent and the concentration depend mainly on the type of the composition and on the coating process. The solvent should be inert, i.e. it should not enter any chemical reaction with the components and it should be removable again during drying after coating. Examples of suitable solvents are ketones, ethers and esters, such as methyl ethyl ketone, 2-heptanone, cyclopentanone, cyclohexanone, γ-butyrolactone, ethyl pyruvate, diethylene glycol dimethyl ether, 2-methoxyethanol, 2-ethoxyethanol, 2-ethoxyethyl acetate, 1-methoxy-2-propyl acetate, 1,2-dimethoxyethane, ethyl acetate and 3-methoxymethyl propionate.

The solution is applied by means of known coating processes uniformly to a substrate, for example by spin-coating, dipping, blade coating, curtain coating methods, brushing, spraying, especially by electrostatic spraying, and reverse roller coating. It is also possible to apply the photosensitive layer to a temporary flexible support and then to coat the final substrate, for example a copper-laminated circuit board, by layer transfer via lamination.

The quantity applied (layer thickness) and the nature of the substrate (layer support) depend on the desired field of application. The layer thickness range comprises in general values from about 0.1 μm to more than 10 μm.

After coating, the solvent is as a rule removed by drying, and the result is a layer of the composition according to the invention of the support.

The radiation-sensitive compositions according to the invention are suitable as photoresists for electronics (electroplating resist, etch resist, solder resist), for the production of printing plates such as offset printing plates or screen printing forms, for use in chemical milling or use as microresist in the production of integrated circuits. The possible layer supports and the processing conditions of the coated substrates are correspondingly diverse.

The use of the compositions according to the invention as a positive photoresist is a further subject of the invention.

Films of polyester, cellulose acetate or plastic-coated papers, for example, are used for photographic information recordings; specially treated aluminium is used for offset printing forms, copper laminates are used for the production of printed circuits, and silicon wafers are used for the production of integrated circuits. The layer thicknesses for photographic materials and offset printing forms are as a rule about 0.5 μm to 10 μm, and 0.4 to about 2 μm for printed circuits.

For producing relief structures, the substrate coated with the composition according to the invention is exposed imagewise. The term "imagewise" exposure comprises exposure through a photomask which contains a predetermined pattern, for example a transparency, exposure by a laser beam which is moved, for example under computer control, across the surface of the coated substrate and generates an image in this way, irradiation with computer-controlled electron beams and also irradiation with X-rays or UV light through an appropriate mask.

The radiation sources used can in principle be all lamps which emit radiation in the UV range. Both point light sources and two-dimensional emitters (lamp carpets) are suitable. Examples are: carbon arc lamps, xenon arc lamps, mercury vapour lamps doped, if appropriate, with metal halides (metal halide lamps), fluorescent lamps, incandescent argon lamps, electronic flash lamps, photographic floodlights, electron beams and X-rays. The distance between the lamp and the image material according to the invention can vary depending on the intended use and the type and/or intensity of the lamp, for example between 2 cm and 150 cm. Laser light sources, for example argon ion lasers or crypton ion lasers, are especially suitable. With laser light, the resist can also be exposed without a mask, the controlled laser beam writing directly on the resist layer. In this case, the high sensitivity of the materials according to the invention is very advantageous, since it allows high writing speeds at relatively low intensity. Printed circuits in the electronics industry, lithographic offset printing plates or relief printing plates as well as photographic image recording materials can be produced by this method. The high sensitivity of the resists is also of advantage for exposure by means of DUV steppers, since very short exposure times are desirable.

After the exposure, the resist is as a rule subjected to a heat treatment, the so-called post-exposure bake, in order to ensure complete reaction of the acid-sensitive groups in the polymer structure with the acid generated by the exposure. The duration and temperature of this post-exposure bake can vary within wide ranges and depend essentially on the composition of the acid-sensitive polymer and on the nature of the acid generator used as well as on the concentrations of these two components. Usually, the exposed resist is subjected for a period from a few seconds up to several minutes to temperatures of about 50°-150° C.

Surprisingly, the delay time, during which T-tops do not yet appear, is substantially extended in the case of the resists according to the invention, as compared with the hitherto known positive photoresist systems, for example those described in EP-A 366 590 or EP-A 342 498.

After the imagewise exposure and heat treatment of the material, carried out in the usual manner, the exposed areas of the photoresist are removed by dissolving them out in a developer.

The selection of the particular developer depends on the nature of the photoresist, in particular on the nature of the binder used or of the photolysis products formed. The developer can comprise aqueous solutions of bases, to which organic solvents or mixtures thereof have been added if necessary.

Particularly preferred developers are aqueous alkaline solutions, such as are also used for the development of naphthoquinone-diazide layers. These include in particular aqueous solutions of alkali metal silicates, phosphates, hydroxides and carbonates. If appropriate, minor quantities of wetting agents and/or organic solvents can also have been added to these solutions.

Typical organic solvents which can be added to the developer fluids are, for example, cyclohexanone, 2-ethoxyethanol, toluene, acetone, isopropanol, ethanol and mixtures of two or more of these solvents.

Apart from the greatly reduced delay time effects, the resist compositions according to the invention are distinguished by good application properties and high optical transparency, high thermal stability and very good resolution power (submicron region).

The protective layers and relief structures produced by using the photoresist compositions according to the invention represent a further subject of the invention.

EXAMPLES 1. Preparation of the polymers

I.1. Terpolymer of 4-(2-tetrahydropyranyloxy)styrene, N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

In a 100 ml round-bottomed flask, 4.1 g (20 mmol) of 4-(2-tetrahydropyranyloxy)styrene, 1.3 g (10 mmol) of N-hydroxymethylmaleimide, 1.7 g (10 mmol) of N-acetoxymethylmaleimide and 0.3 g of dibenzoyl peroxide are dissolved in 30 ml of tetrahydrofuran (THF). The solution is stirred for 4 hours at 60° C. After cooling to room temperature, the polymer is precipitated in 11 of methanol, filtered off and dried. This gives 6.2 g (87%) of a white powder which is characterized as follows:

¹ H-NMR (CDCl₃, 300 MHz): δ=6.3-7.4 ppm (m)

δ=5.1-5.6 ppm (s, broad) δ=4.7-5.0 ppm (s, broad) δ=3.8-4.0 ppm (s, broad) δ=3.5-3.8 ppm (s, broad) δ=1.2-2.3 ppm (m)

By means of gel permeation chromatography (GPC, polystyrene calibration), a molecular weight of M_(n) =13 950 (number average) and M_(w) =47 950 (weight average) is measured, from which a polymolecularity index PD=M_(w) /M_(n) of 3.4 results. The thermogravimetric analysis (TGA, heating rate 10° C./min) shows a weight loss of 32% in the temperature range from 140° to 240° C.

I.2-I.10. Terpolymers of 4-(2-tetrahydropyranyloxy)styrene, N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

analogously to Example I.1., terpolymers are prepared with different monomer rations. The quantities of the starting compounds employed and the yields and measured molecular weights are shown in Table 1 which follows.

                                      TABLE 1                                      __________________________________________________________________________     Terpolymers of 4-(2-tetrahydropyranyloxy)styrene, N-hydroxymethylmaleimide      and N-acetoxymethylmaleimide                                                  Example I.2.  I.3.  I.4.  I.5.  I.6.  I.7.  I.8.  I.9   I.10.                  __________________________________________________________________________     4-(2-Tetra-                                                                            20.4 g                                                                               4.8 g 15.0 g                                                                               5.44 g                                                                               67.7 g                                                                               8.2 g 55.7 g                                                                               56.2 g                                                                               10.88 g                hydro-  (100 mmol)                                                                           (29 mmol)                                                                            (73 mmol)                                                                            (26 mmol)                                                                            (332 mmol)                                                                           (40 mmol)                                                                            (273 mmol)                                                                           (276 mmol)                                                                           (53 mmol)              pyranyloxy)-                                                                   styrene                                                                        N-Hydroxy-                                                                             88.9 g                                                                               1.78 g                                                                               4.7 g 2.03 g                                                                               16.9 g                                                                               2.03 g                                                                               12.1 g                                                                               7.38 g                                                                               2.71 g                 methyl- (70 mmol)                                                                            (14 mmol)                                                                            (37 mmol)                                                                            (16 mmol)                                                                            (132 mmol)                                                                           (16 mmol)                                                                            (95 mmol)                                                                            (58 mmol)                                                                            (21 mmol)              maleimide                                                                      N-Acetoxy-                                                                             5.1 g 1.02 g                                                                               6.2 g 1.81 g                                                                               30.0 g                                                                               4.05 g                                                                               30.0 g                                                                               35.0 g                                                                               4.82 g                 methyl- (30 mmol)                                                                            (6 mmol)                                                                             (37 mmol)                                                                            (11 mmol)                                                                            (177 mmol)                                                                           (24 mmol)                                                                            (177 mmol)                                                                           (207 mmol)                                                                           (28.5 mmol)            maleimide                                                                      Dibenzoyl                                                                              1.5 g 0.3 g 1.0 g 0.4 g 4.97 g                                                                               0.6 g 3.9 g 4.0 g 0.8 g                  peroxide                                                                       THF     150 ml                                                                               30 ml 100 ml                                                                               40 ml 500 ml                                                                               60 ml 420 ml                                                                               400 ml                                                                               80 ml                  Yield   79%   87%   84%   81%   87%   85%   73%   68%   85%                    M.sub.n 5300  14,750                                                                               17,000                                                                               18,100                                                                               7420  10,400                                                                               7250  6300  16,050                 M.sub.w 34,500                                                                               59,200                                                                               56,650                                                                               63,500                                                                               49,700                                                                               54,300                                                                               37,760                                                                               29,500                                                                               70,520                 PD      6.5   4.0   3.3   3.5   6.7   5.2   5.2   4.7   4.4                    __________________________________________________________________________

I.11. Terpolymer of 4-(tert-butylcarbonyloxy)styrene, N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

In an 150 ml round-bottomed flask, 11.0 g (54 mmol) of 4-(tert-butylcarbonyloxy)styrene, 1.6 g (12.5 mmol) of N-hydroxymethylmaleimide, 6.3 g (37.5 mmol) of N-acetoxymethylmaleimide and 0.76 g of dibenzoyl peroxide are dissolved in 80 ml of THF. The solution is stirred for 4 hours at 60° C. After cooling to room temperature, the polymer is precipitated in 11 of methanol, filtered off and then dissolved in 100 ml of THF. This solution is then slowly added to 1 l of a solvent mixture of n-hexane and toluene. The precipitate formed is filtered off and dried, giving 15.2 g (80%) of a white powder.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.2-7.5 ppm (m) δ=5.3 ppm (s, broad) δ=4.8 ppm (s, broad) δ=2.4-3.5 ppm (m) δ=2.0 ppm (s) δ=1.5 ppm (s)

GPC (polystyrene calibration): M_(n) 32 11,950 M_(w) =38,650 PD=3.2

TGA (10° C./min): 27 % weight loss in the range from 130°-180° C.

I.12. Terpolymer of 4-tert-butoxystyrene, N-hydroxymethylmaleimide and N-acetoxymethylmaleimide methylmaleimide

Analogously to Example I.11., 13.9 g (83%) of a white powder are obtained from 8.8 g (50 mmol) of 4-tert-butoxystyrene, 1.6 g (12.5 mmol) of N-hydroxymethylmaleimide, 6.3 g (37.5 mmol) of N-acetoxymethylmaleimide and 0.67 g of dibenzoyl peroxide, dissolved in 80 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ6.2-7.3 ppm (m) δ=5.3 ppm (s, broad) δ=4.8 ppm (s, broad) δ=2.4-3.6 ppm (m) δ=2.0 ppm (s) δ=1.3 ppm (s)

GPC (polystyrene calibration): M_(n) =18,980 M_(w) =65,150 PD =3.4

TGA (10 ° C./min): 20% weight loss in the range from 280°-340° C.

I.13. Terpolymer of 4-(3-methylbut-2-enyloxy)styrene, N-hydroxymethylmaleimide and N-acetoxymethylmaleimide

a) Synthesis of 4-(3-methylbut-2-enyloxy)styrene:

In a 500 ml three-necked flask with internal thermometer, nitrogen blanketing and a magnetic stirrer, 22 g (0.4 mol) of KOH powder in 200 ml of dimethyl sulfoxide are introduced. 12.0 g (0.1 mol) of p-hydroxystyrene are then added in portions at 20° C.; 30.0 g (0.2 mol) of 3,3'-dimethylallyl bromide are then added dropwise at 20° C. After stirring for 30 minutes at 20° C., 100 g of ice are added slowly. The mixture is then extracted twice with 200 ml of ether. The combined organic extracts are washed first with 200 ml of 1N sodium hydroxide solution and then with 200 ml of water and dried over MgSO₄. After removal of the solvent, the remaining residue is distilled in vacuo (0.07 mbar, 80° C.). This gives 15.5 g (82 mmol, 82%) of a colourless oil.

¹ H-NMR (CDCl₃, 300 MHz): δ=b 7.31 ppm (d, 2H) δ=6.85 ppm (d, 2H) δ=6.63 ppm (dd, 1H) δ=5.58 ppm (dd, 1H) δ=5.47 ppm (t, 1H) δ=5.09 ppm (dd, 1H) δ=4.47 ppm (d, 2H) δ=1.86 ppm (s, 3H) δ=1.77 ppm (s, 3H)

b) Synthesis of the terpolymer:

Analogously to Example I.11., 14.73 g (85%) of a white powder are obtained from 9.4 g (50 mmol) of 4-(3-methylbut-2-enyloxy)styrene, 1.6 g (12.5 mmol) of N-hydroxymethylmaleimide, 6.3 g (37.5 mmol) of N-acetoxymethylmaleimide and 0.69 g of dibenzoyl peroxide, dissolved in 75 ml of THF.

¹ H-NMR (CDCl₃, 300 MHZ): δ=6.3-7.4 ppm (m) δ=5.1-5.4 ppm (m) δ=4.4 ppm (s) δ=2.4-3.5 ppm (m) δ=2.0 ppm (s) δ=1.8 ppm (s)

GPC (polystyrene calibration): M_(n) =23,580 M_(w) =235,500 PD=9.9

TGA (10° C./min): 14% weight loss in the range of 260°-320° C.

I.14. Terpolymer of 4-(2-tetrahydropyranyloxy)styrene, N-hydroxymethylmaleimide and N-(2-acetoxyethyl)maleimide

Analogously to Example I.1., 5.4 g (75%) of a white powder are obtained from 4.1 g (20 mmol) of 4-(2-(tetrahydropyranyloxy)styrene, 1.3 g (10 mmol) of N-hydroxymethylmaleimide, 1.8 g (10 mmol) of N-(2-acetoxyethyl)maleimide and 0.3 g of dibenzoyl peroxide, dissolved in 30 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.4-7.3 ppm (m) δ=5.35 ppm (s) δ=4.8 ppm (s) δ=3.9 ppm (m) δ=3.6 ppm (m) δ=1.3-3.0 ppm (m)

GPC (polystyrene calibration): M_(n) =8150 M_(w) =59,100 PD=7.2

TGA (10° C./min): 29% weight loss in the range of 180°-230° C.

I.15. Terpolymer of 4-(2-tetrahydropyranyloxy)styrene, N-hydroxymethylmaleimide and N- (2-methoxyethyl)maleimide

Analogously to Example I.5.2 g (75%) of a white powder are obtained from 4.1 g (20 mmol) of 4-(2-tetrahydropyranyloxy)styrene, 1.3 g (10 mmol) of N-hydroxymethylmaleimide, 1.55 g (10 mmol) of N-(2-methoxyethyl)maleimide and 0.3 g of dibenzoyl peroxide, dissolved in 30 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.4-7.3 ppm (m) δ=5.4 ppm (s) δ=4.8 ppm (s) δ=3.9 ppm (m) δ=3.5 ppm (m) δ=3.2 ppm (m) δ=1.3-2.9 ppm (m)

GPC (polystyrene calibration): M_(n) =6660 M_(w) =54,800 PD=8.2

TGA (10° C./min): 30% weight loss in the range of 150°-240 ° C. I. 16. Terpolymer of 4-(2-tetrahydropyranyloxy)benzyl methacrylate, N-hydroxymethylmaleimide and N-(acetoxymethyl)maleimide

Analogously to Example I.1., 9.3 g (28%) of a white powder are obtained from 21.8 g (79 mmol) of 4-(2-tetrahydropyranyloxy)benzyl methacrylate, 6.3 g (49 mmol) of N-hydroxymethylmaleimide, 5.0 g (30 mmol) of N-(acetoxymethyl)maleimide and 1.0 g of dibenzoyl peroxide, dissolved in 130 ml of THF.

¹ H-NMR (CDCl₃, 300 MHz): δ=6.7-7.4 ppm (m) δ=5.4 ppm (s) δ=4.9 ppm (s) δ=3.8 ppm (m) δ=3.6 ppm (m) δ=0.8-3.0 ppm (m)

GPC (polystyrene calibration): M_(n) =4270 M_(w) =13,030 PD=3.0

TGA (10° .C/min): 27% weight loss in the range of 150°-300° C.

I.17. Terpolymer of 4-(2-tetrahydropyranyloxy)styrene, N-Hydroxymethylmaleimide and N-(acetoxymethyl)maleimide

Analogously to Example I.1., 7.5 g (80%) of a white powder axe obtained from 5.1 g (25 mmol) of 4-(2-tetrahydropyranyloxy)styrene, 0.48 g (4 mmol) of N-hydroxymethylmaleimide, 3.59 g (21 mmol) of N-(acetoxymethyl)maleimide, 0.18 g of dodecanethiol and 0.18 g of bis-azoisobutyronitrile, dissolved in 64 ml of diglyme.

GPC (polystyrene calibration): M_(n) =9700 M_(w) =20,700 PD=2.1

II. Application examples

II.1. Positive photoresist

2 g of the polymer from Example I.14 and 0.1 g of triphenylsulfonium trifluoromethanesulfonate are dissolved in 7 g of cyclopentanone. The solution is filtered and spin-coated at 3000 rpm onto a quartz wafer (3 inches). The coated quartz wafer is then dried for 2 minutes at 120° C. The layer thickness of the film thus obtained is 1 μm. The coated wafer is then exposed imagewise (contact exposure) through a quartz mask with monochromatic radiation of wavelength 254 nm(10 nm half-width) at a dosage of 30 mJ/cm². After exposure, the wafer is subjected on a hotplate for 2 minutes to a temperature of 120° C. and then developed in a 2.38% aqueous tetramethylammonium hydroxide solution, the exposed zones being dissolved out. Structures of 0.5 μm with approximately vertical wall profiles are perfectly resolved without formation of T-topping effects.

II.2. Positive photoresist

1.92 g of the polymer from Example I.17 and 0.08 g of triphenylsulfonium trifluoromethanesulfonate are dissolved in 8.0 ml of methoxypropyl acetate. The solution is filtered through a filter of 0.5 mm pore size and then spin-coated onto a silicon wafer (4 inches), an 850 nm thick resist film resulting after drying at 100° C. for 60 seconds. The coated wafer is then exposed imagewise with radiation of wavelength 248 nm by means of a Canon Excimer Laser Stepper (NA:0.37) at a dosage of 18 mJ/cm². After exposure, the wafer is subjected on a hotplate for 1 minute to a temperature of 110° C. and then developed in a 0.262N aqueous tetramethylammonium hydroxide solution, the exposed zones being dissolved out. In this case, lines/spaces structures of 0.3 μm are resolved with approximately vertical wall profiles, without a residue.

In a second experiment carried out analogously, the heat treatment at 110° C. for 1 minute is not carried out until after waiting for one hour after the exposure. In this case too, lines/spaces structures of 0.3 μm are cleanly resolved, without detectable formation of T-topping effects.

II.3. Positive photoresist

1.92 g of the polymer from Example I.11. and 0.07 g of triphenylsulfonium trifluoromethanesulfonate are dissolved in 18.7 g of cyclopentanone. The solution is filtered through a Teflon filter of 0.2 μm pore size and then spin-coated onto a silicon wafer (100 mm). After heating on the hotplate (60 seconds, 130° C.), a 723 nm thick resist film is obtained. The exposure is carried out in optimum focus, using a 5:1 projection exposure apparatus (NA 0.37, Canon FPA 4500) at a wavelength of 248 nm in exposure steps of 1 mJ/cm². After heating on the hotplate (60 seconds, 120° C.), the exposed wafer is developed for 60 seconds in a 0.262N aqueous tetramethylammonium hydroxide solution. A positive image of the structuring mask is obtained. At an exposure dosage of 16 mJ/cm², sub-half micrometer structures are resolved with steep edges. 

What is claimed is:
 1. A polymer having a molecular weight (weight average) M_(w) from 10³ to 10⁶, comprising recurring structural units of the formulae (I), (IIa) and (IIb) ##STR12## in which R₁ is hydrogen or methyl, Y is a direct bond or a divalent radical of the formula (III) ##STR13## in which Z is a C₁ -C₆ alkylene group bound to the phenyl nucleus,OR₂ is an acid-cleavable radical, in which R₂ is C₄ -C₁₀ tert-alkyl, allyl, cyclohex-2-enyl, C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, trialkylsilyl or a group of the formulae (IV)-(VII) ##STR14## in which R₈ is C₁ -C₆ alkyl, or C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, R₃ and R₄ independently or one another are hydrogen, C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, R₅ and R₆ independently of one another are hydrogen or methyl, X is C₁ -C₆ alkylene and R₇ is C₁ -C₆ alkyl, or C₆ -C₁₄ aryl or C₇ -C₁₆ aralkyl which are unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, C₁ -C₆ alkoxy groups or halogen atoms, or is --CO--R₈ in which R₈ is as defined in formula (IV).
 2. A polymer according to claim 1, comprising recurring structural units of the formula (I), in which R₁, R₃ and R₄ are hydrogen, Y is a direct bond and R₂ is C₄ -C₁₀ tert-alkyl, trimethylsilyl, allyl which is unsubstituted or mono- or poly-substituted by C₁ -C₆ alkyl groups, cyclohex-2-enyl or a group of the formulae (IV)-(VII) in which R₈ is C₁ -C₄ alkyl or phenyl.
 3. A polymer according to claim 1, comprising recurring structural units of the formula (I), in which R₁, R₃ and R₄ are hydrogen, Y is a direct bond and R₂ is tert-butyl, tert-butoxycarbonyl, 3-methylbut-2-enyl or a group of the formula (V).
 4. A polymer according to claim 1, comprising recurring structural units of the formula (IIa), in which R₅ and R₆ are hydrogen and X is methylene.
 5. A polymer according to claim 1, comprising recurring structural units of the formula (IIb), in which R₅ and R₆ are hydrogen, R₇ is C₁ -C₄ alkyl, phenyl or --CO--R₈, in which R₈ is C₁ -C₄ alkyl or phenyl, and X is methylene, ethylene, trimethylene or tetramethylene.
 6. A polymer according to claim 1, comprising recurring structural units of the formula (IIb), in which R₅ and R₆ are hydrogen, R₇ is methyl or acetyl and X is methylene or ethylene.
 7. A polymer according to claim 1, comprising 10-75 mol %, mol % of structural units of the formula (IIa) and 25-90 mol % of structural units of the formula (IIb), relative to 100 mol % structural units of the formula (I).
 8. A polymer according to claim 1, comprising 20-50 mol %, mol % of structural units of the formula (IIa) and 50-80 mol % of structural units of the formula (IIb), relative to 100 mol % structural units of the formula (I). 